The present invention relates to decolorizable ink which can be decolored after it is printed and a printer using the ink.
In recent years, the amount of various kinds of information has significantly increased by spread of office automation, and so the level of information output has also increased. The information output is represented by display output and hard copy output from a printer onto paper sheets. The display output, however, requires a large scale circuit board in a display unit. This brings about problems of portability and cost. Regarding the hard copy output, a large quantity of paper as a recording medium is being consumed with increase in the information output amount. Therefore, the hard copy output is expected to be a problem with respect to conservation of natural resources. In addition, recycling of paper sheets once printed by a printer or a copying machine is expensive, since much of a bleaching agent and water are required for the recycling. Under such a situation, it is considered to decrease consumption of paper substantially by using decolorizable ink to print information on a paper sheet, restoring a blank sheet of paper by decoloring the ink, and reusing the paper sheet.
Heretofore, ink which can be decolored on heating has been proposed in, for example, Published Unexamined Japanese Patent Application No. 7-81236. The ink includes a color former such as a leuco dye, a developer, and a organophosphoric compound having a decoloring power.
When such ink is used, however, decoloring can be done insufficiently and, as a result, a paper sheet is hard to return to the blank state. For this reason, decolorizable ink cannot have been put into practical use.